Scramjet isolator

ABSTRACT

A scramjet engine with a novel isolator is disclosed herein. The scramjet includes an air inlet configured to receive and direct air into the engine and a combustor operable to receive air from the air inlet and combust fuel therein as is conventional. An isolator is positioned between the air inlet and the combustor. The isolator includes a primary flow path separated into a plurality of separate secondary flow channels formed therethrough. The smaller secondary flow channels prevent shockwaves from propagating upstream from the combustor to the inlet that can occur during some operating conditions of a supersonic combustion flow process.

Pursuant to 37 C.F.R. § 1.78(a)(4), this application claims the benefitof and priority to prior filed Provisional Application Ser. No.63/195,349, filed Jun. 1, 2021, which is expressly incorporated hereinby reference.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

TECHNICAL FIELD

The present disclosure generally relates to an isolator for a scramjetengine and more particularly, but not exclusively to an isolatordesigned to minimize the size of the scramjet engine.

BACKGROUND

Scramjet propulsion systems do not have turbomachinery components thatare used in turbojet systems. By removing the compressor, the turbineand supporting components, air is free to pass through the enginesubstantially unimpeded. This translates into higher mass flow, higherspeeds, and higher thrust output. This thrust can be increased to propelthe aircraft to fly at both high supersonic and hypersonic speeds. Inthe lower speed regime, between Mach 4 and 8, the combustion ischaracterized by a dual-mode combustion. In dual-mode combustionoperation, the pressure rise generated by heat-release in the combustorcan propagate upstream of fuel injection in the form of a shockwaves.These shockwaves are better known as a pre-combustion shock train. Thisshock train can detrimentally affect the operation of the air inlet bycausing the inlet to unstart. Unstart is an event where the shock traintravels into and out of the inlet causing engine mass capture loss whichcan lead to decreased engine performance or even engine blowout. Onemethod to mitigate this problem is to install an isolator duct betweenthe inlet and the combustor. The isolator duct can reduce the chancethat the shock train will trigger inlet unstart. The length of theisolator duct depends on the aircraft operating flight envelop.

FIG. 1 shows a schematic representation of a prior art scramjet poweredvehicle. In this illustration, airflow is compressed by shockwaves inthe inlet, and is then transported to the combustor at supersonicspeeds. Combustion of fuel with the incoming air generates a large localpressure rise and separation of the boundary layer on the surfaces ofthe combustor duct. This aerodynamic separation can cause pressureperturbations that feed upstream of the point of fuel injection and actsto further compress the core flow thus the generation of theshock-train. As mentioned above, this shock train can cause problems bytriggering inlet unstart.

An isolator positioned in the scramjet flow path upstream of thecombustor can contain the shock train and stop it from disrupting theoperation of the inlet. At relative low Mach (below Mach 8) scramjetoperating conditions, the flow downstream of the shock train can bedecelerated to subsonic speeds prior to it entering the combustionchamber. In this instance, the core flow must then be re-acceleratedthrough Mach 1 by generating what is called a thermal throat. A thermalthroat is produced via a balance between combustor heat release andcombustor area increase. The combination of subsonic and supersonic flowthrough the combustion chamber is known as dual-mode combustion.Dual-mode combustion can produce large pressure levels in the combustorand nozzle, generating high levels of thrust. This flow is affected bymany parameters, including the Mach number entering the isolator fromthe inlet, the state of the boundary layer in the isolator, the areadistribution of the combustor, and the fuel injection strategy. Atspeeds above Mach 8, the increased kinetic energy of the airflow throughthe engine means that the combustion generated pressure rise is notstrong enough to cause boundary layer separation thus keeping the shocktrain from propagating upstream. The core airflow remains supersonicthroughout the engine thus operating in scramjet mode. In this instance,an isolator is no longer needed and the presence of it causesconsiderably higher viscous losses as supersonic flow passes through itthus decreasing overall engine thrust.

The structure of the shock train is of interest in the design ofscramjet isolators. FIG. 2 is a schematic illustration of a prior artisolator where the shock train is imposed on the incoming supersonicairflow. If there were no boundary layer, a normal shock would form in aplane. However, the presence of an incoming boundary layer produces aseries of normal and/or oblique shocks that spreads the pressure riseover a given length thus forming the shock train. In literature, theshock train can also be described as a “pseudo shock”, which ischaracterized by a region of separated flow next to the wall, togetherwith a supersonic core that experiences a pressure gradient due to thearea restriction of the separation, forming a series of crossing obliqueshocks in the core flow. A mixing region also grows between the core andseparated flows, balancing the pressure rise in the core against theshear stress on the boundary of the separation. Finally, the flowreattaches at some point and mixes out to conditions that match thebackpressure. Being able to predict the length scale of the shock trainis the key component of isolator design for dual-mode scramjets. Someexisting systems that use these prior art isolator ducts have variousshortcomings. For example, the isolator becoming a viscous drag penaltyat higher speeds (as mentioned above) and excessive weight penalty ifthe isolator is generally too long for a given flight envelop. Optimallyminimizing isolator length for a given flight envelop is one way toimprove upon an isolator's shortcoming or minimizing isolator lengthwith a new novel isolator design would be another way to improve uponits shortcomings. Accordingly, there remains a need for furthercontributions in this area of technology.

SUMMARY

One embodiment of the present disclosure includes a unique isolator fora scramjet engine. Other embodiments include apparatuses, systems,devices, hardware, methods, and combinations include an isolator havinga plurality of flow paths that operate to reduce the length of theisolator required to prevent aerodynamic interference with airflowpassing upstream through an inlet. Further embodiments, forms, features,aspects, benefits, and advantages of the present application shallbecome apparent from the description and figures provided herewith.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a view of a prior art aircraft powered by a scramjet engineaccording to a prior art embodiment;

FIG. 2 is a cross sectional view of an isolator according to a prior artembodiment;

FIG. 3 is a cross sectional view of an aircraft powered by a scramjetengine according to one embodiment of the present disclosure;

FIG. 4 is a side cross sectional view of an isolator according to oneembodiment of the present disclosure; and

FIG. 5 is an end view of the isolator shown in FIG. 4 .

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended. Any alterations and further modificationsin the described embodiments, and any further applications of theprinciples of the invention as described herein are contemplated aswould normally occur to one skilled in the art to which the inventionrelates.

Referring to FIG. 3 , there are illustrated some aspects of anon-limiting example of a scramjet aircraft 10 that may be operable witha scramjet engine 12 illustrated in the exemplary embodiment. Thescramjet aircraft 10 is operable at speeds of approximately Mach 3 andabove. The illustrated scramjet engine 12 includes a substantiallyrectangular inlet and exhaust, however in other embodiments the scramjetengine 12 may have any cross sectional shape integrated with theaircraft 10, such as by way of example and not limitation, a circularcross section. The aircraft 10 includes a forward fuselage 20 and anempennage 30. In some forms, the empennage may include a traditionaltail assembly 32 that includes a tail 34, vertical stabilizer 36 and anelevator 38. In other forms, the aircraft may not include a traditionaltail assembly such as those of a flying wing or the like. The wings ofthe aircraft are not shown in this cross sectional view, but can be ofany design operable in high Mach number flight as one skilled in the artwould understand.

The scramjet engine 12 includes an air inlet 40 with a converging region50 to compress the high Mach airflow to a high pressure without using atraditional axial compressor. A combustor 60 is positioned downstream ofthe inlet 40 where fuel injectors 62 inject a fuel to combust with thecompressed air. The high pressure and high temperature exhaust productsexiting the combustor 60 are expanded and accelerated through an exhaustnozzle 70 to provide the thrust required to propel the aircraft 10 atspeeds of Mach 4 and greater. An isolator 100 can be positioned betweenthe inlet 40 and the combustor 60 to provide increased operability ofthe scramjet system.

Referring now to FIGS. 4 and 5 , a cross sectional view of an isolator100 and an end view of an isolator 100 according to one non-limitingembodiment are depicted. The isolator 100 extends between a first orforward end 102 and a second or aft end 104. A first flange 103 mayproject from the forward end 102 and a second flange 105 may projectfrom the aft end 104 to connect with components of the engine 12 in theupstream and downstream directions. The flanges 103, 105 may includemechanical fasteners (not shown) or other attachment means such as weldor braze to connect engine components together.

The isolator 100 includes an outer perimeter wall 106 extending betweenthe first and second ends 102, 104, respectively. The outer perimeterwall 106 includes an inner surface 108 to define the outer flow boundaryfor the airflow passageway. A plurality of separate secondary flowchannels 112 are formed internal to the isolator 100. The number ofsecondary channels can vary depending on the engine size or flightenvelop requirements of the aircraft, however in the depicted embodimentthere are three separate secondary channels 112.

A plurality of longitudinal channel walls 114 extend along a length ofthe isolator 100 to separate and form one side of each of the secondarychannels 112. The plurality of longitudinal channel walls 114 can beconnected together to form a central pointed tip 120 extending towardthe forward end 102 at a central location of the isolator housing 100.Each of the channel walls 114 extend between a leading edge 122 and atrailing edge 124 thereof. In some forms, the leading edge 122 can bedefined by a knife edge that projects along an arcuate path between theinner surface 108 of the outer perimeter wall 106 and the centralpointed tip 120. The knife-edge formed at the leading edge 122 of eachlongitudinal wall 114 and the central pointed tip 120 are configured toreduce shock losses of the hypersonic flow velocities of the air movingthrough the scramjet engine 12 at supersonic speeds. The trailing edge124 of the secondary flow channels 112 terminates at the aft end 104 ofthe Isolator 100. The longitudinal channel walls 114 can be furtherdefined by an arcuate sidewall 126 that extends between the innersurface 108 of the outer perimeter wall 106 of the isolator housing 100.The arcuate sidewalls 126 extend between opposing edge walls 128 formedon each of the channel walls 114. The edge walls 128 of the channelwalls 114 can be connected to the inner surface 108 of the isolatorhousing 100. The arcuate sidewalls 126 and the inner surface 108 of theisolator housing 100 cooperate to form a substantially elliptical crosssectional flow area through the secondary flow channels 114. It shouldbe understood that the disclosed embodiment depicts three secondary flowchannels, however in other embodiments a different number of flowchannels may be incorporated such as 2, 4 or more. The cross sectionalshapes of the flow area con be modified by changing the shape of theinner surface 108 of the isolator housing 100 and the side-walls 126 ofthe channel walls 114.

In one aspect, the present disclosure includes a scramjet enginecomprising: an air inlet configured to receive and direct air into theengine; a combustor operable to receive air from the air inlet andcombust fuel therein; an isolator defined by a housing extending betweenfirst and second ends, the isolator positioned between the air inlet andthe combustor; and wherein the isolator includes a primary flow pathseparated into a plurality of separate secondary flow channels formedtherethrough.

In refining aspects, the scramjet engine further comprises a pluralityof channel walls extending along at least a portion of a longitudinallength of the isolator to form the secondary flow channels; a centralpointed tip extending from the plurality of channel walls toward thefirst end of the isolator; wherein the central pointed tip directsairflow from the inlet to the secondary flow channels; wherein each ofthe plurality of channel walls extend between a first edge wall and asecond edge wall to define a sidewall thereof; wherein the first andsecond edge walls engage an inner perimeter wall of the isolatorhousing; wherein the sidewalls of the channel walls are curved in alateral direction between first and second edge walls; wherein thecurved channel walls and an inner perimeter wall of the isolator housingcooperate to form an elliptical cross sectional flow area through thesecondary channel flow paths; wherein the central tip is terminatesdownstream of the first end of the isolator housing; and wherein thecentral tip is terminates upstream of the first end of the isolatorhousing.

Another aspect of the present disclosure includes an isolator for ascramjet comprising: a housing having a longitudinal length extendingbetween a forward end and an aft end; wherein the forward end receivesairflow from an air inlet; wherein the aft end discharges airflow to acombustor; and a plurality of separate flow channels formed internal tothe housing configured to direct airflow therethrough.

In refining aspects, the isolator further comprises a plurality ofinternal channel walls configured to form the flow channels within thehousing; a pointed tip extending from the internal walls toward theforward end of the housing; wherein the pointed tip projects past theforward end of the housing; wherein each of the internal channel wallsinclude a sidewall with an arcuate shape in a lateral direction betweenan opposing pair of edge walls; wherein the edge walls of each channelwall engage with an internal wall of the housing; wherein the internalwall of the housing is arcuate in cross section; and wherein a crosssectional shape of the separate flow channels are substantiallyelliptical.

In another aspect, the present disclosure includes a method foroperating a scramjet comprising: receiving airflow into an engine inletat a speed of at least Mach 3; compressing the airflow through theinlet; splitting the airflow into a plurality of smaller flow paths inan isolator; discharging the airflow from the isolator into a combustor;injecting fuel into the combustor; combusting the fuel; and acceleratingan exhaust byproduct through a nozzle at supersonic speeds. In refiningaspects, the method further comprises minimizing and/or preventingupstream shock wave propagation through the isolator using the pluralityof smaller flow paths formed therein.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the spirit of theinventions are desired to be protected. It should be understood thatwhile the use of words such as preferable, preferably, preferred or morepreferred utilized in the description above indicate that the feature sodescribed may be more desirable, it nonetheless may not be necessary andembodiments lacking the same may be contemplated as within the scope ofthe invention, the scope being defined by the claims that follow. Inreading the claims, it is intended that when words such as “a,” “an,”“at least one,” or “at least one portion” are used there is no intentionto limit the claim to only one item unless specifically stated to thecontrary in the claim. When the language “at least a portion” and/or “aportion” is used the item can include a portion and/or the entire itemunless specifically stated to the contrary.

Unless specified or limited otherwise, the terms “mounted,” “connected,”“supported,” and “coupled” and variations thereof are used broadly andencompass both direct and indirect mountings, connections, supports, andcouplings. Further, “connected” and “coupled” are not restricted tophysical or mechanical connections or couplings.

What is claimed is:
 1. A scramjet engine comprising: an air inletconfigured to receive and direct air into the scramjet engine; acombustor operable to receive air from the air inlet and combust fueltherein; an isolator defined by a housing extending between first andsecond ends, the isolator positioned between the air inlet and thecombustor; wherein the isolator includes a primary flow path separatedinto a plurality of separate secondary flow channels formedtherethrough; and a plurality of channel walls extending to the secondend of the isolator to form the plurality of separate secondary flowchannels.
 2. The scramjet engine of claim 1, further comprising acentral pointed tip extending from the plurality of channel walls towardthe first end of the isolator.
 3. The scramjet engine of claim 2,wherein the central pointed tip directs airflow from the inlet to theplurality of separate secondary flow channels.
 4. The scramjet engine ofclaim 3, wherein the central pointed tip terminates downstream of thefirst end of the isolator housing.
 5. The scramjet engine of claim 3,wherein the central pointed tip terminates upstream of the first end ofthe isolator housing.
 6. The scramjet engine of claim 2, wherein each ofthe plurality of channel walls extend between a first edge wall and asecond edge wall to define a sidewall thereof.
 7. The scramjet engine ofclaim 6, wherein the first and second edge walls engage an innerperimeter wall of the housing.
 8. The scramjet engine of claim 6,wherein the sidewalls of the plurality of channel walls are curved in alateral direction between first and second edge walls.
 9. The scramjetengine of claim 8, wherein the plurality of channel walls and an innerperimeter wall of the housing cooperate to form an elliptical crosssectional flow area through the plurality of separate secondary channelflow paths.
 10. An isolator for a scramjet comprising: a housing havinga longitudinal length extending between a forward end and an aft end;wherein the forward end receives airflow from an air inlet; wherein theaft end discharges airflow to a combustor; a plurality of separate flowchannels formed internal to the housing configured to direct airflowtherethrough; a plurality of internal channel walls configured to formthe plurality of separate flow channels within the housing; a pointedtip extending from the plurality of internal channel walls toward theforward end of the housing; and wherein the pointed tip projects pastthe forward end of the housing.
 11. The isolator of claim 10, whereineach of the plurality of internal channel walls include a sidewall withan arcuate shape in a lateral direction between an opposing pair of edgewalls.
 12. The isolator of claim 11, wherein the edge walls of each ofthe plurality of internal channel walls engage with an internal wall ofthe housing.
 13. The isolator of claim 12, wherein the internal wall ofthe housing is arcuate in cross section.
 14. The isolator of claim 10,wherein a cross sectional shape of the plurality of separate flowchannels are substantially elliptical.
 15. A scramjet engine comprising:an air inlet configured to receive and direct air into the scramjetengine; a combustor operable to receive air from the air inlet andcombust fuel therein; an isolator defined by a housing extending betweenfirst and second ends, the isolator positioned between the air inlet andthe combustor; wherein the isolator includes a primary flow pathseparated into a plurality of separate secondary flow channels formedtherethrough; a plurality of channel walls extending along at least aportion of a longitudinal length of the isolator to form the pluralityof separate secondary flow channels; wherein each of the plurality ofchannel walls extend between a first edge wall and a second edge wall todefine a sidewall thereof; and wherein the sidewalls of the plurality ofchannel walls are curved in a lateral direction between first and secondedge walls.
 16. An isolator for a scramjet comprising: a housing havinga longitudinal length extending between a forward end and an aft end;wherein the forward end receives airflow from an air inlet; wherein theaft end discharges airflow to a combustor; a plurality of separate flowchannels formed internal to the housing configured to direct airflowtherethrough; and wherein a cross sectional shape of the plurality ofseparate flow channels are substantially elliptical.